1. Field of the Invention
This invention pertains generally to the field of wrapping machines and more particularly to machines adapted to receive articles and to form and close a wrapping of heat sealable material about the articles.
2. Description of the Prior Art
A variety of consumer articles are mass production wrapped in heat sealable wrapping material before being delivered to the customer. A common example is paper toweling rolls wrapped in polyethylene, in which the wrapper serves to hold the roll together and to protect it from moisture and abrasion. The heat seals on the wrappers for such paper toweling thus must be substantially moisture tight to perform adequately.
As is generally the case for products prepared for the consumer mass market, the cost per unit article is strongly dependent on the amount of time required for each operation, including packaging. The typical paper roll wrapping machine requires that the rolls be displaced from their direction of motion several times during the packaging operation to produce a sealed overwrap of heat sealable material around the roll, and then to fold and heat seal the ends of the packaging about the roll. The displacements and reciprocations of the roll within the machine limits the production speed because of the time that must be allocated to such motions. Additionally, the motions of the machine parts required to change the direction of motion of the articles invariably leads to shock and vibration which can become severe as machine speed is increased.
Known machines capable of forming sealed wrappers around articles are shown in U.S. Pat. Nos. 1,320,699; 2,296,142; 2,550,616; 2,584,060; 3,001,351; and 3,110,142. The production of sealed packages around articles with these machines generally requires speed limiting changes in the direction of motion of the articles.
Additional known patents which disclose the formation of a heat sealed wrapper about an article are U.S. Pat. Nos. 2,545,243; 2,982,334; 3,011,934; 3,050,916; 3,133,390; 3,153,607; 3,325,331; 3,576,694; 4,054,474; 4,084,999; and B417,299. In the typical mechanism for heat sealing polyethylene or other heat sealable material into a tube, a back-up die is usually required to hold the material firmly against the sealing die. The space occupied by the back-up die tends to inhibit formation of a tight wrap if the tube is formed around the articles being wrapped. Alternatively, if the tube is sealed before the articles are inserted, the additional steps involved increase the processing time.